Safety switch

ABSTRACT

A safety switch includes a base having two terminals connected thereto and each terminal has a first contact point and a bimetallic plate is movably received in the base and has two second contact points which are located above the two first contact points. The two ends of the bimetallic plate can be bent when overflow. A first spring is biased between an inside of the base and the bimetallic plate. A button assembly is connected to the base and a second spring is biased between the button assembly and the bimetallic plate. The two ends of the bimetallic plate bend upward to cut off the circuit when current overflows.

FIELD OF THE INVENTION

The present invention relates to a switch that cuts the circuit by usinga bimetallic plate when overload and no fuse or breaker is required.

BACKGROUND OF THE INVENTION

A conventional switch known to applicant is disclosed in FIGS. 1 and 2and generally includes a base 1 with two terminals 7 and a conductiveplate 27. The two terminals 7 each have a first contact point 9 and theconductive plate 27 has two second contact points 271 which are loweredto contact the first contact points 9 by pushing a button assembly 25. Afirst spring 11 is biased between the inside of the base 1 and theconductive plate 27 and a second spring 23 is biased between the buttonassembly 25 and the conductive plate 27, wherein the first spring 11 hasa larger spring force than the second spring 23 so that the conductiveplate 27 is located at a position as shown in FIG. 1. When pushing thebutton 252 of the button assembly 25, the conductive plate 27 is loweredand the second contact points 271 contact the first contact points 9 asshown in FIG. 2. The conductive plate 27 is raised by the first spring11 when the button 252 is pushed again and released by the operation ofthe mechanism of the button assembly 25. This switch cannot respond whenthe current overflows so that many safety switches are developed, suchas U.S. Pat. Nos. 5,786,742, 5,223,813, 4,937,548, 4,661,667, 5,223,813,4,931,762, 5,451,729, and 4,704,594. A common shortcoming of the safetyswitches is that there is a complicated mechanism involved in each baseand most of them is suffered by a problem of delay response.

Therefore, it is desired to have a safety switch that requires only asimple structure which responses the current overflow so as to cut offthe circuit.

SUMMARY OF THE INVENTION

In accordance with an aspect of the present invention, there is provideda safety switch that comprises a base having two terminals and eachterminal has a first contact point. A bimetallic plate is movablyreceived in the base and two second contact points are connected to twoends of the bimetallic plate. The two second contact points are locatedabove the two first contact points and the two ends of the bimetallicplate can be bent when overflow. A first spring is biased between aninside of the base and the bimetallic plate. A button assembly isconnected to the base and a second spring is biased between the buttonassembly and the bimetallic plate. The two second contact points on themetallic plate are removed from the first contact points when themetallic plate is bent.

The present invention will become more obvious from the followingdescription when taken in connection with the accompanying drawings,which show, for purposes of illustration only, a preferred embodiment inaccordance with the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a conventional switch;

FIG. 2 is a cross-sectional view of the conventional switch wherein thebutton is pushed to bring the second contact points to contact the firstcontact points;

FIG. 3 is an exploded view to show a safety switch in accordance withthe present invention;

FIG. 4 shows that a button of the safety switch of the present inventionis pushed to bring second contact points to contact first contactpoints, and

FIG. 5 shows that two ends of a metallic plate are deformed when thecurrent overflows.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to the drawings and in particular FIGS. 3 and 4, a safetyswitch of the present invention comprises a base 10 having two chambers3 for receiving two terminals 7 respectively and each terminal 7 has afirst contact point 9. A first spring 11 is rested in a recess 5 locatedbetween the two chambers 3 and a lower end of a support post 13 isbiased by the first spring 11. A bimetallic plate 15 has a hole 17defined through a center thereof and a top end of the support post 13extends through the hole 17 and is connected to a cap 21. Two secondcontact points 19 are connected to two ends of the bimetallic plate 15and the two second contact points 19 are located above the two firstcontact points 9. The bimetallic plate 15 includes a bending line 151 atthe center thereof so that the two ends of the bimetallic plate 15 maybend when overflow.

A button assembly 25 is connected to a top of the base 10 and a secondspring 23 is biased between the button assembly 25 and the bimetallicplate 15. The button assembly 25 includes a main body 253 which has apassage defined therein and the passage has a plurality of longitudinalgrooves 2531 defined in an inner periphery thereof. A button 252 ismovably inserted in the passage and has several triangular protrusionsextending from a lower end thereof. Each triangular protrusion includesa stop 2521 on an outside thereof. A core piece 251 has a top endinserted in the open bottom of the button 252 and has several ridges2511 on an outer periphery thereof. Each ridge 2511 has an inclinedsurface which contacts a side of the corresponding triangular protrusionof the button 252. The lower end of the core piece 251 contacts thesecond spring 23 so that when pushing the button 252 downward, thebimetallic plate 15 is brought to let the second contact points 19contact the first contact points 9 as shown in FIG. 4. Pushing thebutton 252 again, the bimetallic plate 15 is brought by the secondspring 23 and the button 252 goes up to its original position.

As shown in FIG. 5, when overflow, the two ends of the bimetallic plate15 is deformed upward about the bending line 151 and the second contactpoints 19 are disengaged from the first contact points 9 so as to cutoff the circuit and protect the switch from being burned. If the button252 is pushed again, the first spring 11 pushes the center of thebimetallic plate 15 upward which contacts the projections 100 on aninside of the base 10 and the two ends of the bimetallic plate 15 isbent downward again. If the user pushes the button 252 again, thebimetallic plate 15 is moved as shown in FIG. 4 to connect the circuit.

The safety switch needs only one button assembly 25 and the bimetallicplate 15 is deformed when overflow. The safety switch requires a simplestructure and this reduces the manufacturing cost and the response timeis shorter than the conventional switches.

While we have shown and described the embodiment in accordance with thepresent invention, it should be clear to those skilled in the art thatfurther embodiments may be made without departing from the scope of thepresent invention.

What is claimed is:
 1. A safety switch comprising: a base having twoterminals connected thereto and each terminal having a first contactpoint; a bimetallic plate movably received in the base and two secondcontact points connected to two ends of the bimetallic plate, the twosecond contact points located above the two first contact points and thetwo ends of the bimetallic plate being bent when overflow; a firstspring biased between an inside of the base and the bimetallic plate,and a button assembly connected to the base and a second spring biasedbetween the button assembly and the bimetallic plate.
 2. The safetyswitch as claimed in claim 1, wherein the bimetallic plate is supportedon a support post at a center of the bimetallic plate and the firstspring is biased between an inside of the base and a lower end of thesupport post.
 3. The safety switch as claimed in claim 2, wherein thebimetallic plate has a hole defined through a center thereof and a topend of the support post extends through the hole and is connected to acap, the second spring is biased between the cap and the buttonassembly.